The requirements imposed on ball and socket joints of this class include especially high specific loadability and low bearing clearance under both static and dynamic loads as well as low break-away and operating torque, as well as a low maintenance requirement or absence of need for maintenance over the service life of the motor vehicle or ball and socket joint, the lowest possible weight and a low space requirement for installation. In addition, manufacture shall be as cost-effective as possible.
Such a ball and socket joint is known, for example, from DE 101 63 147 A1. This ball and socket joint has a hollow cylindrical joint housing, in the interior space of which a ball shell made of plastic is inserted for receiving the joint ball arranged on a ball pivot in a slidingly movable manner. The ball shell of the ball and socket joint disclosed in the document is supported in the axial direction of the joint housing by means of two circumferential collars on the front sides of the joint housing.
The first of the two circumferential collars is already from the outset made integrally in one piece with the plastic ball shell in this prior-art ball and socket joint, while the second collar of the ball shell located opposite the first collar is manufactured in the prior-art ball and socket joint for geometric reasons only after the ball shell has been introduced into the joint housing of the ball and socket joint.
In other words, the ball shell is introduced—together with the ball pivot already arranged therein—into the housing during the assembly of the prior-art ball and socket joint such that the first collar is supported on a first, mostly ball pivot-side front surface of the housing. The second collar arranged on the opposite side of the housing in relation to the first collar is then prepared from the previously still projecting ring collar of the ball shell by means of a shaping process. The document being cited suggests thermal shaping or ultrasound shaping for shaping the ring collar into the collar.
However, it was found that such a design of the anchoring of the plastic ball shell in the joint housing does not always meet the increasing requirements imposed on loadability, failure safety and weather resistance in ball and socket joints of this class. In particular, loosening of the ball shell in the joint housing may develop over the service life of the ball and socket joint. Undesired relative motions may thus develop between the joint housing and the ball shell, which may lead to wear especially of the ball shell in the area of the outer circumference thereof as a consequence of the friction associated therewith as well as as a consequence of the entry of dirt between the ball shell and the joint housing, as a result of which the ball and socket joint may eventually fail prematurely.
To solve this problem, it is proposed in the document DE 101 63 147 A1 to arrange elevations and/or depressions, for example, inner corners, edges or furrows in the area of the inner jacket surface of the joint housing over the entire height of the housing. The ball shell, which has a certain oversize compared to the joint housing, and which has, without any change, an essentially cylindrical outer jacket surface, is then introduced or pressed into the interior space of the joint housing during the assembly of the ball and socket joint. The outer jacket surface of the ball shell is plastically deformed during this pressing-in operation corresponding to the relief or shaping of the inner jacket surface of the joint housing to a certain extent, as a result of which improved, positive-locking connection is obtained between the joint housing and the ball shell.
However, it was found that corrosion continued to develop between the outer jacket surface of the ball shell and the inner jacket surface of the joint housing in joint housings of such a design with elevations and depressions arranged on the inner jacket surface for positive-locking connection with the ball shell. As the applicant has determined, this is due especially to the fact that water or dirt continued to be able to enter between the ball shell and the joint housing precisely because of the elevations and depressions that were continuous over the entire height of the joint housing.
The collars of the ball shell, which are arranged on the front side at both ends of the joint housing, are also unable to completely prevent this. This is linked, on the one hand, with the fact that a sufficient axial prestress of the ball shell in the joint housing cannot always be guaranteed after the shaping of the projecting ring collar of the ball shell into the collar. On the other hand, these leaks between the ball shell and the joint housing are linked, as the applicant found out, especially with the fact that due to the elevations and depressions arranged in the joint housing over the entire height thereof, the contact surface available for the corresponding collar of the ball shell often lacks a sufficiently large size and smoothness.
The quality of the beading of the ring collar of the ball shell into the collar, which is frequently carried out by means of ultrasound, is also potentially compromised because of the depressions and elevations on the inner jacket surface of the joint housing, which are continuous up to the two front sides of the joint housing, which may likewise compromise the anchoring of the ball shell in the joint housing as well as the tightness of the gap between the joint housing and the ball shell.
Another disadvantageous effect of the continuous elevations and depressions arranged on the inner jacket surface of the joint housing, which occurs in the ball and socket joints known from the state of the art, is that these elevations and depressions are prepared in the state of the art only later, for example, by means of embossing or broaching, on the joint housing manufactured in advance.
Elevations of varying heights and depressions of varying depths frequently develop along the circumference of the joint housing on the inner jacket surface of the joint housing during this subsequent preparation of the elevations and depressions either because of inaccuracies and tolerances of the subsequent operation or because of differences in the accumulation of material, which occur already during the manufacture of the blank for the joint housing. Such different elevations or depressions and run-outs of the joint housing may then lead to an irregular or increased prestress between the ball shell and the joint ball of the ball and socket joint.
This also leads again, besides the binding of the ball and socket joint associated therewith, to increased wear of the joint and hence to a reduction of the service life of the ball and socket joint or entails the risk of premature failure of the ball and socket joint, which cannot be accepted, especially in case of safety-relevant applications, for example, in a motor vehicle.
In other words, this means that a plastic ball shell fixed in this manner in the joint housing by means of continuous elevations and depressions is often no longer able to meet the currently existing requirements imposed on ball and socket joints in terms of compliance with the intended moments of friction and service life requirements when further stressing effects, for example, intense vibrations, corrosive media and/or abrasives such as dirt or sand particles act on the ball and socket joint during the use of such ball and socket joints.